getId KeyError: None - When Saving

OK, it turns out this issue was coming from images that were included in the RichText fields of the item. These images had broken image paths (not handled in the migration) and required manually checking the fields and updating the image 'resolveuid' paths with the corresponding updated image path format used in Plone 5. In this case something like '/@@images/image/thumb' or the sorts...
This was the script I ran: fix image scales from archetypes scales to dx scales, old scale names to new scale names · GitHub
Just a note for future persons who might have this issue!

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